1. Field of the Invention
The present invention generally relates to an oxidation catalyst unit for a wet-type electrophotographic printer. More particularly, the present invention relates to an oxidation catalyst unit for oxidizing and thereby removing a carrier vapor generated in a fusing unit, a method for controlling the oxidation catalyst unit, and a wet-type electrophotographic image forming apparatus having the oxidation catalyst unit.
2. Description of the Related Art
An electrophotographic image forming apparatus scans a laser beam onto a photoconductive medium to form an electrostatic latent image, and transfers a visible image formed by attaching a developer onto the electrostatic latent image, thereby printing out a desired image. A wet-type electrophotographic image forming apparatus uses a liquid developer while a dry-type one uses a powder toner. The wet-type electrophotographic image forming apparatus produces a clearer image and high-quality color images can be obtained.
The developers consist of a toner and a liquid carrier, such as norpar. Norpar is a hydrocarbon-based solvent, which is a mixture of C10H22, C11H24, C12H26, and C13H28.
A paper onto which the developer is transferred passes through a fusing unit during which the toner component in the developer is fixed onto paper. When fused, liquid carrier, such as norpar, in the developer is vaporized by high temperature and discharged outward in the form of a hydrocarbon gas such as CH4.
The hydrocarbon gas is a volatile organic compound (VOC), which emits an offensive odor when discharged. Therefore, various methods for removing hydrocarbon gas have been introduced.
Conventional methods for removing hydrocarbon gases include the filtration, direct combustion, and catalytic oxidation methods. The filtration method physically removes gaseous components using a carbon filter, such as an active carbon filter. The direct combustion method combusts gaseous components at an ignition point of approximately 600° C. to 800° C. The catalytic oxidation method combusts gaseous components at a relatively lower temperature of approximately 150° C. to 400° C. using a catalyst, thereby oxidizing and resolving the components into water and carbon dioxide.
In the filtration method, the carbon filter does not have the capability of resolving the entrained carrier vapors. Therefore, the carbon filter becomes saturated with carrier vapors and needs to be replaced when the carrier vapors are entrained over a predetermined amount in the carbon filter, and such replacement needs to be done frequently. Furthermore, the direct combustion method is not safe due to the high temperature generated. Due to above the problems, the wet-type electrophotographic image forming apparatuses have mainly employed the catalytic oxidation method for removing the carrier vapors.
FIG. 1 is a schematic view of a conventional oxidation catalyst unit. The oxidation catalyst unit 160 comprises a duct 161, a suction fan 162, a heater 163, an oxidation catalyst carrying medium 164, and a controller 165. The controller 165 comprises a driving part 165a for driving the suction fan 162 and a power part 165b for supplying electric power to the driving part 165a. 
The duct 161, which is connected to one side of a fusing unit 150, guides the carrier vapor V into the oxidation catalyst unit 160 to remove the carrier vapor V produced in the fusing unit 150. This occurs when paper P moves through the fusing rollers 151 and 152.
The suction fan 162 is mounted in the duct 161 to forcibly send the carrier vapor V toward the oxidation catalyst carrying medium 164.
The heater 163 raises the temperature of the carrier vapor V to an activating temperature, for example, 200° C. The oxidation catalyst carrying medium 164 carries a catalyst such as Pt and Pd, which catalyzes the oxidization reaction. The oxidation catalyst carrying medium 164 is mounted behind the heater 163.
The suction fan 162 of the conventional oxidation catalyst unit 160, which draws in the carrier vapor V, rotates at a uniform velocity. The velocity of the suction fan 162 is determined or set based on the maximum amount of carrier vapor V. The maximum amount of carrier vapor V is mainly caused when printing a whole-color image.
FIG. 2 is a graph illustrating the fan velocity of the oxidation catalyst unit 160 of FIG. 1 according to the amount of image data. Referring to FIG. 2, whether printing a text image, which causes a relatively small amount of the carrier vapor V (FIG. 1), or a whole-color image, which causes a relatively larger amount of the carrier vapor V (FIG. 1), the suction fan 162 (FIG. 1) operates at the maximum velocity N. Therefore, the suction fan 162 (FIG. 1) is constantly applied with a load regardless of the amount of image data, and accordingly, the noise and vibration of the suction fan 162 increases due to the overload. In addition, power is wasted.
The above problems also occur when the temperature of the heater 163 in the oxidation catalyst unit 160 is set corresponding to the maximum amount of the carrier vapor V without regard to the actual amount of the carrier vapor V, or when the velocity of a cooling fan (not shown) of the image forming apparatus is always set corresponding to the maximum amount of the carrier vapor V without regard to the actual amount of the carrier vapor V.
Accordingly, there is a need for an oxidation catalyst unit wherein the heater temperature or the cooling fan velocity is set corresponding to the actual amount of carrier vapor V.